The menu object needs to be defined first.

boil_kettle/boil_kettle.ino

@@ -64,6 +64,15 @@ void doEncoder()
 
 }
 
+// LCD menu setup.
+
+LiquidLine KettleState_line(0, 0, "Boil Kettle      ", KettleState);
+LiquidLine kettle_power_line(0, 1, "Kettle Power %   ", KettleDuty);
+
+LiquidScreen home_screen(KettleState_line, kettle_power_line);
+
+LiquidMenu menu(lcd);
+
 void UpdateBoilKettle(){
   static byte last_kettle_duty = 0;